A turbidimeter measures the turbidity of a liquid sample in a sample cuvette or vial. A nephelometric turbidimeter determines the concentration of solid particles suspended in a liquid sample within a sample cuvette by projecting a light beam into the liquid sample within the cuvette. A light detector detects the amount of light scattered by the suspended solid particles in a cone of solid angle, e.g., of 30° centered at 90° to the light beam axis.
If the light detector of a turbidimeter detects light scattered in one single sector of the circumference (of the cuvette, vial or sample vessel), the signal of the light detector is relatively low because much scattered light is being thrown away. Circular mirrors and/or prism arrangements have been designed to coaxially surround the liquid sample cuvette in an effort to direct radially scattered light (over the complete) circumference to the light detector. Such designs generally are acknowledged to increase the signal to noise ratio (SNR). However, many of these devices are sensitive to geometrical inaccuracies of their optical arrangements (directing the scattered light toward the light detector) and may be sensitive to non-homogenous samples (turbidity differences in the liquid sample).